perjury
lying under oath
[U] Uncountable
This term carries a heavy legal weight and a strong moral stigma, specifically tied to the betrayal of a sworn oath. It is not used for general lying or deception in social settings, but is strictly reserved for formal legal proceedings where a person has been legally bound to tell the truth. The connotation is one of calculated dishonesty and a direct assault on the integrity of the judicial system.
Grammatically, this noun is uncountable. You cannot refer to a single instance as a perjury; instead, you must use partitive constructions such as an act of perjury or a count of perjury when referring to specific occurrences in a legal case.
Used as a legal concept or a crime, such as stating that perjury is a felony.